The present invention relates generally to the transport and handling of articles being subjected to vacuum processes, and, more specifically, to the transport and handling of integrated circuit wafers being processed in vacuum chambers, such as by evaporation, vapor deposition, sputtering, plasma etching and the like.
Integrated circuits, most commonly formed on either silicon (Si) semiconductor or gallium arsenide (GaAs) wafer substrates, are commonly subjected to one or more process steps within a vacuum chamber in the course of forming a large number of replicas of an integrated circuit on each wafer. In order to avoid having to vent the vacuum processing chamber each time one or more wafers is loaded into or removed from the processing chamber, and then re-establish a vacuum before processing can begin, the wafers are moved through an intermediate load lock chamber. The load lock chamber is connected to the vacuum chamber through a gate valve, and has another gate valve opening to the outside. The pressure within the load lock chamber is controllable independently of that in the processing chamber.
Wafers or other articles to be processed are loaded into the processing chamber by first moving them into the load lock chamber through its outside gate valve while the gate valve connecting the two chambers remains closed. The processing chamber is maintained at or very near its processing pressure during loading and unloading. The outside gate valve is then closed with the articles in the load lock chamber, and the pressure within the load lock chamber is reduced to a level about equal to that of the vacuum chamber. The gate valve between the chambers is then opened and the articles moved into the processing chamber through that gate valve. This gate valve is then closed and the articles in the processing chamber are processed. These steps are performed in a reverse order when removing articles from the processing chamber to the outside through the load lock chamber. The load lock chamber is vented after the articles are moved into it from the processing chamber when the load lock chamber is at the reduced pressure of the processing chamber. Some vacuum processing machines have two load lock chambers connected by separate gate valves to the processing chamber in order to increase the throughput of wafers processed, one load lock chamber being used for loading and the other for unloading.
According to one aspect of the present invention, briefly and generally, a load lock chamber having a very small volume is formed within the processing chamber by a wall that is moveable into the processing chamber to unseal the load lock chamber for allowing articles to be moved between it and the processing chamber. In a preferred form, the wall is oriented horizontally and also serves as a carrier for the wafers or other articles being processed. In this arrangement, the wall moves up and down within the processing chamber to both close and open the load lock chamber to the processing chamber. In an upward position, the wall forms a seal that isolates the load lock chamber from the processing chamber. In a lowered position, the wall unseals the load lock chamber from the processing chamber and positions the articles carried by it for easy transfer to the processing chamber.
According to another aspect of the present invention, briefly and generally, a technique and mechanism are provided for moving articles between two positions, such as between one position in the load lock chamber (either that described above or a conventional load lock chamber) and another position in the processing chamber. Rather than moving each article one at a time, articles at the two positions are swapped by a common rotary motion of the mechanism. In order to minimize the area required for the rotary motion, the articles to be exchanged are preferably first moved close together with an axis of rotation positioned between them. The small amount of area taken by the rotation is a particular advantage for transferring articles between the load lock chamber and the processing chamber, since this allows the chamber to be made smaller.
An advantage of the mechanism that simultaneously swaps the positions of two articles is that the throughput of the vacuum processing is increased. When used to transfer articles between the load lock chamber and the processing chamber, a processed article is moved out of the processing chamber into the load lock chamber and a fresh article is moved at the same time from the load lock chamber into the processing chamber. The same technique can be used with another transfer mechanism to simultaneously remove a processed article from the load lock chamber to the outside and load a fresh unprocessed article from the outside into the load lock chamber. According to a further aspect of the present invention, these simultaneous transfers increase the amount of parallelism in the processing of the wafers or articles.
In one specific application of the load lock chamber and article moving mechanism, they are included in machines that evaporate material onto wafers within the vacuum processing chamber. The wafers are held on a domed shape wafer carrier during the evaporation. Since the wafers can be very fragile, it is preferred to move the wafer carrier, with wafers attached, into and out of the processing chamber, rather than moving the individual wafers. Since such domed carriers can be quite large and awkward to move, according to a further aspect of the present invention, briefly and generally, the domed surface may be divided into wedge shaped segments that are removably held on a circular frame. These segments are moved one at a time between a frame maintained in the processing chamber and one in the load lock chamber. This keeps low the weight and size of the items being transferred. Another feature, in order to further minimize the area necessary to swap locations of two such dome pieces, their pointed ends may be truncated without significant loss of wafer carrying capacity.
For situations where a high throughput of the systems described above is unnecessary, a simpler and lower cost article transfer mechanism may be used within the vacuum processing chamber of the type described above in the first paragraph of this Summary. According to yet another aspect of the present invention, therefore, a carriage is moved back and forth between positions under the load lock chamber and the processing area within the vacuum chamber, in order to transfer articles between these two positions. The carrier for the wafers or other articles being processed, which also serves as a removable load lock chamber wall, is lowered onto and raised from the carriage from below by an elevator structure that passes through an opening in the carriage. This elevator structure retracts below the carriage when the carriage is being moved.